A novel coronavirus (SARS-COV-2) pneumonia caused multiple infections in the central Chinese city, Wuhan, and it has been shown to have human-to-human transmission and sustained human-to-human transmission characteristic, which is a new risk to public health. Although the time between the onset of the disease and seeking medical attention is now generally shorter, with 27% of patients seeking medical attention within two days of onset, but at least 89% of patients are not hospitalized until the fifth day of illness (9). Because pneumonia is the common characteristic of SARS-COV-2 infection, and it is a concern that the course of disease development of pneumonia in COVID-19 patients. Applying CT examination to the COVID-19 patients or suspected patients is an effective way to evaluate patient's condition. And some cases with positive chest CT findings may present with negative results of real time reverse-transcription–polymerase chain- reaction (RT-PCR) for SARS-COV-2, but these patients were eventually confirmed with SARS-COV-2 infection by repeated swab tests (10,11). Chest CT scan is an important inspection method. Early the pulmonary inflammatory lesions present as multiple small patchy and interstitial change, lesions in the lung periphery is obvious. Then inflammatory lesions develop into multiple infiltrates ground glass opacity, seriously even appear consolidation in the lung (12). Elderly people over 60 years old may be accompanied by other basic diseases, which will make pneumonia progress faster, while young people under 60 years old have fewer basic diseases, and pneumonia changes are less affected by other diseases. Our study showed that the CT scores and length of maximum pulmonary inflammatory lesions in the young and middle-aged patients under 60 years old with COVID-19 was statistically different between the different duration time of initial symptoms groups. The duration of the initial symptom was found to be positively correlated with the CT score of pulmonary lesions and the length of the largest inflammatory lesions in the lungs. The longer the duration of the initial symptom was, the higher the CT score was, the more serious the CT manifestations of pulmonary lesions were, the larger the lesions were.
Viruses are common causes of respiratory infections. The imaging manifestations of viral pneumonia are diverse and overlap with other infectious and inflammatory pulmonary diseases (13). Viruses in the same virus family have similar pathogenesis. Since the outbreak of Severe Acute Respiratory Syndrome (SARS) in 2002 and Middle East Respiratory Syndrome (MERS) in 2012, the possibility of coronavirus transmission from animals to humans has been confirmed (14). SARS-COV-2 is similar to the pathological process of SARS and MERS. Peripheral lung involvement was observed in SARS and MERS patients, ground glass opacity and consolidation were the main CT manifestations. The CT findings of SARS usually included ground glass opacity and consolidation in areas of unilateral or bilateral lung (15). The role of thin-slice CT in recording SARS parenchymal anomalies has also been demonstrated when chest radiographs show normal or only suspicious anomalies (16, 17). In this study, CT examination of COVID-19 patients showed that the lesions were mostly located in the peripheral pulmonary zone and were presented as localized or multiple patchy ground glass opacity or solid lesions. Since the viral infection was mainly interstitial lesions, there was no trend of pulmonary segments and subsegment distribution. Other studies (12) suggested that there was no significant difference in lobar or craniocaudal distribution of the novel coronavirus pneumonia.
CT findings of pulmonary inflammatory are related to the development of inflammatory pathology. In the early stage of the disease, localized inflammatory infiltration of both sides of the lungs was commonly observed, which was the most of ground glass opacity under the pleura. The early stage lung tissues showed different degree of alveolar injury, including alveolar congestion, inflammatory exudation and formation of hyaline membrane (18). Therefore, the CT manifestations showed thin ground glass opacity, and crazy-paving pattern or reticulation changes were formed when the lesions accompanied by pulmonary interstitial edema. The main CT manifestations in the progressive stage were increased number of lesions and expanded range, gradually involving multiple lobes in lung, and consolidation or co-existence of consolidation and ground glass opacity. Irregular consolidation is often associated with a large number of exfoliated epithelium and foam cells in the alveoli, inflammatory cell infiltration, inflammatory exudation filling the alveolar cavity. Consolidation tissues may be accompanied by capillary congestion and necrosis of lung tissue and alveoli (19). After the onset of initial symptom, the pulmonary lesions gradually developed from normal or blurred ground glass opacity to solid opacity. The CT score showed that the overall pulmonary inflammatory lesions increased after the duration of initial symptom increased, and CT scores were higher in the group of initial symptom duration ≥3 days. The longer the duration of the initial symptom was, the more pneumonia infiltration and expansion will occur, and the more consolidation changes will occur.
The main symptom of SARS patients included fever, general discomfort, muscle pain, fatigue and head ache, and some patients in the acute phase might had viremia (20). The main symptom of COVID-19 patients was fever. In this study 60.6% of the patients had initial symptoms of fever. Other initial symptoms included diarrhea or a sore throat, etc. The correlation analysis showed that the duration of initial symptoms of patients was positively correlated with the CT score of pulmonary inflammatory lesions. The initial symptom duration of pneumonia may be used to evaluate disease progress, and it was associated with the size of the largest lesions. Therefore, patients with fever or other symptoms should be paid attention to. In this study, it was suggested that most of the lung lesions were blurred ground glass opacity dominated within 7 days after the initial symptoms, accounting for 57.6%. The inflammatory lesions were relatively mild, while main consolidation or multiple consolidation accompanied by ground glass opacity accounted for 1/3. Gaik et al. (21) showed that within the 1st week after onset of symptoms, the main abnormalities included ground glass opacities (ten [56%] of 18) and consolidation (eight [44%] of 18). Ground glass opacities alone or with superimposed interlobular septal thickening were most commonly found in the 1st week after onset of symptoms. Previous studies demonstrated that consolidation lesions on CT of viral pneumonia had a more severe clinical course than those with ground glass opacity, which might be related to further diffuse alveolar damage in the solid lesions (22). The longer the initial symptoms, the more pulmonary lesions will progress, so early treatment is of great importance for patients to control the disease.
There were several limitations in our study. First, this was a retrospective study and the number of patients enrolled was small. Only 33 young and middle-aged COVID-19 patients with CT imaging. We limited our study to chest CT, because CT was more sensitive to early or mild disease. However, in medical front lines, chest radiography may also serve as a screening tool in areas with high disease prevalence and limited resources. Second, the study was only conducted during early and mild stage, and study in the acute phase of SARS-COV-2 was missed. It is necessary to further study the imaging manifestations of severe or treated patients in the future to enrich the imaging studies of SARS-COV-2.
In conclusion, we revealed a potential positive correlation between the duration of the initial symptoms and the degree and size of pneumonia lesions. Most of the early lesions were ground glass opacity.